In a liquid crystal display device capable of displaying a color image, in general, each pixel is divided into three sub-pixels: a red color pixel provided with a color filter that allows red color light to pass through; a green color pixel provided with a color filter that allows green color light to pass through; and a blue color pixel provided with a color filter that allows blue color light to pass through. The provision of the color filters on the respective three sub-pixels makes it possible to display color images. However, the color filters absorb as much as about two thirds of backlight incident on a liquid crystal panel. This results in a problem that the liquid crystal display device of the color filter type is low in light use efficiency. Thus, a liquid crystal display device of a field sequential system in which a color is displayed without using a color filter has attracted attention.
In general, in the liquid crystal display device using the field sequential system, one frame period in which one screen is displayed is divided into three fields. Note that although the field is also called a subframe, the field is used as the term throughout all the following description. For example, one frame period is divided into a field (red color field) in which a red color screen is displayed based on a red color component of an input image signal, a field (green color field) in which a green color screen is displayed based on a green color component of the input image signal, and a field (blue color field) in which a blue color screen is displayed based on a blue color component of the input image signal. By displaying the primary colors alternately such that one of the primary colors is displayed at a time as described above, a color image is displayed on a liquid crystal panel. In the liquid crystal display device of the field sequential system, the color image is displayed in the above-described manner, and thus the color filters are unnecessary. Therefore, in the liquid crystal display device of the field sequential system, it is possible to achieve light use efficiency about three times higher than that achieved by the liquid crystal display device of the color filter type. Therefore, the liquid crystal display device of the field sequential system is suitable for increasing luminance or reducing power consumption.
Note that in the present description, a combination of a data value of a red color component, a data value of a green color component, and a data value of a blue color component is referred to as an “RGB combination”. For example, “R=128, G=32, B=255” is an example of an RGB combination. In this example, the data value of the red color component is 128, the data value of the green color component is 32, and the data value of the blue color component is 255. The data value is typically given by a gradation value.
In the liquid crystal display device, an image is displayed by controlling a transmittance of each pixel by controlling a voltage (a voltage applied to the liquid crystal). Regarding this, as illustrated in FIG. 22, it takes several milliseconds for the transmittance to reach a target transmittance after writing of data into a pixel (application of a voltage) is started. Therefore, in the liquid crystal display device of the field sequential system, in each field, backlight of a color corresponding to the field is switched from an off-state to an on-state after the liquid crystal has responded to a certain degree. That is, in the liquid crystal display device of the field sequential system, the backlight is in the on-state only during a part of a second half period of each field (for example, during a period denoted by a symbol T9 in FIG. 22).
Furthermore, in the liquid crystal display device, there is a possibility that a slow response of a liquid crystal makes it difficult to obtained a high image quality, for example, when a moving image is displayed. To handle the low response of the liquid crystal, it is known to use a driving method called over driving (overshoot driving). In the over driving method, depending on a combination of a data value of an input image signal of an immediately previous frame and a data value of an input image signal of a current frame, a driving voltage higher than a gradation voltage predetermined for the data value of the input image signal of the current frame or a driving voltage lower than the gradation voltage predetermined for the data value of the input image signal of the current frame is applied to the liquid crystal panel. That is, the over driving allows the input image signal to be corrected such that a temporal change (not a spatial change) of the data value is emphasized. In the liquid crystal display device of the color filter type, the over driving is performed such that the liquid crystal responds so as to reach the target transmittance within each frame.
In relation to the present invention, Japanese Unexamined Patent Application Publication No. 7-121138 discloses a technique related to a liquid crystal display device of the field sequential system. In the technique disclosed in Japanese Unexamined Patent Application Publication No. 7-121138, the timing of scanning a time-division three primary color light emission device is delayed by an amount corresponding to an optical response time of a liquid crystal, and there is provided a no-light-emission period corresponding to the optical response time of the liquid crystal. Furthermore, when data is written to a pixel, a gamma correction is performed depending on a result of a comparison between data of a previous field and data of a current field.